#include<iostream>
using namespace std;
int main()
{
	double a=1, b=2, c,d=0.5,i=1;
	while (i < 21)
	{
		a = b;
		b = b + i;
		c = b / a;
		d = d + c;
		i = i + 1;
	}
	cout << d;

}